Question 834596
You have 4L of an 90% aqueous solution of hydrochloric acid. You want 1L of a 25% solution. How much of the stock solution do you need to use?
<pre>
You are going to add water to the stock solution to make 1 liter.
Make this chart:

                 |         |           | Liters of
                 |Liters of|   Percent | pure acid 
                 | liquid  |    Acid   | contained
---------------------------------------------------
stock solution   |   x     |  90%=0.90 |   0.90x           
---------------------------------------------------
water            |  1-x    |   0%=0.00 | 0.00(1-x)  
===================================================
final solution   |   1     |  25%=0.25 |  0.25(1)

        {{{(matrix(10,1,

Number,of, liters,of,pure,acid,contained,in,stock,solution))}}}{{{""+""}}}{{{(matrix(10,1,

Number,of, liters,of,pure,acid,contained,in,water,"(none!)"))}}}{{{""=""}}}{{{(matrix(10,1,

Number,of, liters,of,pure,acid,contained,in,final,solution))}}}
 
                             {{{0.90x}}}{{{""+""}}}{{{0.00(1-x)}}}{{{""=""}}}{{{0.25(1)}}}

                                  {{{0.90x}}}{{{""+""}}}{{{"0"}}}{{{""=""}}}{{{0.25}}}

                                      {{{0.90x}}}{{{""=""}}}{{{0.25}}}

                                      {{{0.90x/0.90}}}{{{""=""}}}{{{0.25/0.90}}}

                                          {{{x}}}{{{""=""}}}{{{25/90}}}

                                          {{{x}}}{{{""=""}}}{{{5/18}}}

Answer:  {{{5/18}}}ths of a liter of stock solution, and {{{13/18}}}ths of a liter of water.

Edwin</pre>